For a considerable time various types of machines for the so-called "instantaneous" production of coffee, that is of caffe espresso, have been known, these machines incorporating a grinder for the metered grinding of the coffee beans. In general, the known machines are constituted of a grinding-metering unit delivering a metered quantity of ground powder, a boiler unit for heating the water and the coffee unit by means of a thermosiphon system or by direct contact, a water metering unit either of an electrical type with a probe or a piston and cylinder type, and an electrically driven pump for generating the required water pressure.
These machines in general are based upon the principle of expelling the used pellet by means of a suitable movement of the lower filter (coffee delivery filter); in some cases, a system of levers and cams which actuates the lower filter and the upper closure tap is used for this movement, while in other cases a hydraulic system controlled by electrically operated valves is used. In such machines, the grinding and metering of the coffee are effected by operating the grinder by means of a timer which predetermines the dose on the basis of the operating time, or by interlocking the motor of the grinder with a metering device which operates a pallet, which acts upon a microswitch actuated by the ground coffee. These known types of automatic machines with boilers, which continuously maintain pressurised water at about 100.degree. C., exhibit various disadvantages in practical use, including: the requirement of safety-valves on the boiler with inevitable loss of water and steam, the necessity for removing lime from the water by suitable purifiers and also a complex electrical installation.
It is an object of the present invention to provide an improved automatic machine for the production of coffee, particularly caffe espresso or other less concentrated type of coffee from beans in which the disadvantages referred to above are materially reduced. It is a further object of the present invention to provide an improved automatic machine for the production of coffee which is of such electrical and mechanical simplicity as to avoid the requirement of specialized maintenance personnel.
It is another object of the invention to provide a highly efficient and safe machine, of limited bulk, free from electrical and hydraulic servomechanisms and capable of operating constantly and regularly over a significant period of time.